In an optical transmission device (that may be referred to as an optical transmission station) of an optical communication system, one light source may be shared between an optical transmitter and an optical receiver. The optical transmission device may, for example, include an optical branching circuit that branches the output light of the light source into transmission light for the optical transmitter and local light for the optical receiver.
Related techniques are disclosed in, for example, Japanese Laid-open Patent Publication Nos. 2015-170916, 2013-145942, 2015-167174, 2016-082590, 2014-236420 and 2004-029341.